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v5 Written and Lab: UDLD, CDP, LLDP Notes

v5 Written:
2.1.b Impelment and troubleshoot layer 2 protocols
2.1.b [i] CDP, LLDP
2.1.b [ii] UDLD

v5 Lab:
1.1.b Implement and troublshoot layer 2 protocols
1.1.b [i] CDP, LLDP
1.1.b [ii] UDLD


Catalyst 3750-X and 3560-X Softward Configuration Guide, Cisco IOS Release 15.0(1)
Chapter 28, Configuring CDP, pgs. 28-1 to 28-5

Catalyst 3750-X and 3560-X Softward Configuration Guide, Cisco IOS Release 15.0(1)
Chapter 30, Configuring LLDP, LLDP-MED, and Wired Location Service, pgs. 30-1 to 30-12

Catalyst 3750-X and 3560-X Softward Configuration Guide, Cisco IOS Release 15.0(1)
Chapter 31, Configuring UDLD, pgs. 31-1 to 31-7



Cisco Discovery Protocol (CDP)
– runs over Layer 2 (data link layer)
– used by all Cisco devices
– sends periodic messages to a multicast address
– advertises at least one IP address that can receive SNMP messages
– advertisements contain time-to-live or holddown information

Default CDP Configuration
– CDP global state: enabled
– CDP interface state: enabled
– CDP timer: 60 seconds
– CDP holdtime: 180 seconds
– CDP Version-2 advertisements: enabled

conf t
cdp timer
cdp holdtime
cdp advertise-v2

show cdp

To disable CDP globally:

conf t
no cdp run

To disable CDP on an interface:

conf t
int fa0/1
no cdp enable

Monitoring CDP

clear cdp counters
clear cdp table

show cdp
show cdp entry
show cdp int fa0/1
show cdp neighbors
show cdp neighbors fa0/1 detail
show cdp traffic

Link Layer Discovery Protocol (LLDP)
– supports non-Cisco devices and allow interoperability between those devices
– neighbor discovery protocol
– runs over the data link layer
– LLDP attributes are called TLVs (type, length, value descriptions)

Basic management TLVs:
– Port description TLV
– System name TLV
– System description TLV
– System capabilities TLV
– Management address TLV

Default LLDP Configuration
– LLDP global state: disabled
– LLDP holdtime: 120 seconds
– LLDP timer: 30 seconds
– LLDP reinitialization delay: 2 seconds
– LLDP tlv-select: disabled to send an receive all TLVs
– LLDP interface state: disabled
– LLDP receive: disabled
– LLDP transmit: disabled
– LLDP med-tlv-select: disabled to send all LLDP-MED TLVs

If the interface is configured as a tunnel port, LLDP is automatically disabled

conf t
lldp run

conf t
int fa0/1
lldp transmit
lldp receive

show lldp

conf t
lldp holdtime
lldp reinit
lldp timer
lldp tlv-select
lldp med-tlv-select

show lldp

LLDP Media Endpoint Discovery (LLDP-MED)
– Extension to LLDP that operates between endpoint devices such as IP Phones
– Provides support for VOIP applications

Additional LLDP-MED TLVs:
– MAC / PHY configuration / status TLV
– LLDP-MED capabilities TLV
– Network policy TLV
– Power management TLV
– Inventory management TLV
– Location TLV

Monitoring LLDP

clear lldp counters
clear lldp table

show lldp entry
show lldp interface
show lldp neighbors
show lldp neighbors fa0/1 detail
show lldp traffic

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